The nuclear receptor (NR) superfamily comprises more than 150 different proteins, most of which are believed to function as ligand activated transcription factors, exerting widely different biological responses by regulating gene expression (for review, see Di Croce et al, EMBO J18:6201-6210 (1999); Mangelsdorf, et al Cell 83:825-839 (1995); Perlmann, et al, Cell 90:391-397 (1997)). Members of this family include receptors for endogenous small, lipophilic molecules, such as steroid hormones, retinoids, vitamin D and thyroid hormone.
The classical steroid receptors include the mineralocorticoid receptor (MR) (or aldosterone receptor), the estrogen receptors, ER alpha and ER beta, the androgen receptor (AR), the progesterone receptor (PR) and the glucocorticoid receptor (GR). Also closely related in structure are the estrogen related receptors (ERRs) ERR1, ERR2 and ERR3. The steroid receptors perform important functions in the body related to the transcriptional homeostasis of electrolyte and water balance, growth, development and wound healing, fertility, stress responses, immunological function, and cognitive functioning (see, Assay Drug Dev. Technol., 1 (6): 843-52 (2003)). Accordingly, compounds that modulate (i.e. antagonize, agonize, partially antagonize, partially agonize) the activity of steroid nuclear receptors are important pharmaceutical agents that have specific utility in a number of methods, as well as for the treatment and prevention of a wide range of diseases and disorders modulated by the activity of steroid nuclear receptors.
Members of the steroid nuclear receptor sub-family exhibit significant homology to each other and possess closely related DNA and ligand binding domains. Given the close similarity in ligand binding domains of the steroid nuclear receptors, it is not surprising that many naturally occurring and synthetic molecules possess the ability to modulate the activity of more than one steroid nuclear receptor. For example the naturally occurring glucocorticoids cortisol and corticosterone are able to modulate both the glucocorticoid receptor and the mineralocorticoid receptor under physiological conditions.
Accordingly, one approach to developing compounds that are steroid nuclear receptor modulators is to identify a core chemical scaffold that exhibits a common structural motif that provides for the ability to bind to a steroid nuclear receptor, and which in certain embodiments possesses the ability to selectively modulate one or more of the other steroid nuclear receptors. Such compounds are useful for the local or systemic treatment or prophylaxis of human and veterinary diseases, disorders and conditions that are modulated, or otherwise affected by one or more steroid nuclear receptors, or in which steroid nuclear receptor activity, is implicated.
A well-characterized example of the classical steroid receptor sub-family that is amenable to this approach is the mineralocorticoid receptor (aldosterone receptor). The mineralocorticoid receptor plays an important role in regulating electrolyte balance and blood pressure in the body (Adv. Physiol. Educ., 26(1): 8-20 (2002), and its activity is modulated in vivo through the secretion of aldosterone.
Traditionally, it was thought that aldosterone was secreted by the zona glomerulosa of the adrenal gland in response to angiotensin II, potassium and adrenocorticotropic hormone (ACTH), and acted primarily on the epithelial cells of the kidney and colon to regulate sodium and potassium transport. More recently, it has been appreciated that aldosterone is also synthesized by endothelial cells and in vascular smooth muscle cells (VSMCs), the brain, blood vessels and myocardium where it may play a paracrine or autocrine role (Ann. N.Y. Acad. Sci. 970 89-100 (2002)).
Tissue specificity for aldosterone is conferred by the local expression of the mineralocorticoid receptor and by the activity of 11-beta hydroxysteroid dehydrogenase type 2 (11 β-HSD2), which acts to convert the cross-reactive glucocorticoids cortisol and corticosterone into cortisone and 11-dehydrocorticosterone which have significantly reduced affinity for the MR (Science, 242: 583-585 (1988)).
In humans, elevated plasma aldosterone concentrations are usually associated with hypertension, typically mediated through the effect of the hormone on sodium retention and blood volume. Hypertension affects about 5 million Americans, approximately a third of which are unaware of their condition and are not receiving treatment. Hypertension is associated with the development of cardiovascular, cardiac and renal diseases, including chronic and congestive heart failure (J. Postgrad. Med. J., 79 :634-642 (2003)), progressive renal failure (J. Am. Soc. Nephrol. 14 :2395-2401 (2003)) and chronic and end stage renal failure (Am. J. Kid. Dis., 37 (4): 677-688 (2001)). In these conditions, elevated blood pressure appears to enhance and amplify the progressive decline in organ function in these diseases.
Aldosterone also has direct effects on brain, heart, vascular and renal tissues. In the heart, vascular and renal tissues, aldosterone action can also play a significant role in the development and progression of inflammation, scarring and fibrosis (the generation of fibrotic tissue) independently of the effects on blood pressure (Clin. Cardiol., 23:724-730 (2000); Adv. Physiol. Educ., 26(1): 8-20 (2002); Hypertension, 26:101-111 (1995)).
In the brain, aldosterone has been linked to various cognitive dysfunctions, and aldosterone antagonists have been shown to be useful for improving cognitive function (US Application UA2002/0111337), and treating cognitive & mood dysfunctions.
In chronic heart failure (CHF), impaired cardiac function triggers a train of compensatory mechanisms, including aldosterone secretion, that ultimately leads to a worsening of symptoms and reduced survival (J. Clin. Endo & Meta, 88: (6) 2376-2383 (2003)). These changes are primarily mediated by the renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system. Activation of the RAAS leads to increases in renin, angiotensin II and aldosterone. Angiotensin II acts as a vasoconstrictor, promotes aldosterone production, and stimulates norepinephrine release from sympathetic nerve terminals to increase the heart rate. Aldosterone acts to increase blood volume, and hence blood pressure, through its action in the kidney to retain sodium.
While the net effect of these factors is to restore blood pressure, the increased peripheral vascular resistance also increases the load against which the heart works. Ultimately the increased cardiac pressure results in cardiac re-modeling, leading to lung stiffness, pulmonary edema, and breathlessness. Additionally peripheral vasoconstriction results in reduced blood flow to the skeletal muscles contributing to fatigue during exercise.
Current drug treatments for CHF are focused on relieving the symptoms of the disease, improving the quality of life, slowing disease progression, preventing hospital admission, prolonging active life, and reducing mortality. Such therapeutic approaches include the use of diuretics, angiotensin converting enzyme inhibitors (ACE inhibitors), beta adrenergic receptor blockers (beta blockers), AT antagonists and calcium channel blockers to suppress the harmful effects of the neuroendocrine compensatory mechanisms such as the RAAS and beta adrenergic (symphathetic) nervous system. (Postgrad. Med. J. 79 634-642 (2003)).
Diuretics act to reduce water retention, reduce blood pressure and can act as vasodilators to reduce circulatory resistance. ACE inhibitors and beta blockers have been shown to reduce mortality and improve symptom status in CHF in part by reducing angiotensin II and aldosterone levels. However angiotensin II and aldosterone typically return to normal levels with chronic therapy. Accordingly, angiotensin II receptor antagonists, which selectively block the AT1 angiotensin receptor, and aldosterone antagonists, which selectively block the mineralocorticoid receptor, provide significant therapeutic benefit for the treatment of CHF (Circulation, 100:1056-1064 (1999); N. Eng. J. Med., 341 (10):709-718 (1999)).
In addition to aldosterone and angiotensin II, calcium channels play an important role in heart failure. In both vascular and cardiac tissue, muscle cell contraction occurs when cells are depolarized from the influx of calcium through calcium channels in the cell. Calcium channel blockers inhibit muscle contraction and promote relaxation. In vascular smooth muscle this results in vessel dilation, reduced blood pressure (anti-hypertensive effect) and a reduction in the force required to pump blood by the heart. Calcium channel blockers also act on the heart to improve filling by promoting relaxation of cardiac muscle in diastole. However, calcium channel blockers also reduce the force of contraction during systole (negative inotropy) and therefore are often not the drug of choice for treating heart failure.
Hypertension is not only a primary cause of the development of cardiovascular, cardiac and renal diseases, but a risk factor for the progression of these diseases initiated by other mechanisms such as atherosclerosis, cardiovascular disease, ischemic heart disease, diabetes, diabetic nephropathy, chronic glomerulonephritis and polycystic kidney disease (J. Am. Soc. Nephrol., 14 :2395-2401 (2003)).
In renal failure, as with the case of chronic heart failure, a number of clinical trials have established that interruption of the RAAS cascade with ACE inhibitors is beneficial in limiting renal disease (Am. J. Kid. Dis., 37 (4): 677-688 (2001). Additional studies have also established that aldosterone antagonists can attenuate proteinuria and renal damage typically observed in progressive renal disease and offer further therapeutic benefit compared to ACE inhibitors alone (Hypertension., 31:451-458 (1998)).
Many aldosterone antagonists are known. For example spironolactone, the first approved aldosterone antagonist, has been used for blocking aldosterone-dependent sodium transport in the distal tubule of the kidney in order to reduce edema and to treat essential hypertension and primary hyperaldosteronism (F. Mantero et al, Clin. Sci. Mol. Med., 45 (Suppl 1), 219s-224s (1973)). Spironolactone is also used commonly in the treatment of other hyperaldosterone-related diseases such as liver cirrhosis, renal failure and congestive heart failure (F. J. Saunders et al, Aldactone; Spironolactone: A Comprehensive Review, Searle, N.Y. (1978)).
However, spironolactone is not very selective for the MR over other steroid receptors, including the androgen and progesterone receptors. This cross reactivity leads to undesired side effects such as menstrual irregularity in women, and gynecomastia in men (Circulation, 107 :2512-2518 (2003)). Eplerenone is a derivative of spironolactone that is more selective for the MR than spironolactone (Nature Reviews, 2: 177-178 (2003)). However, eplerenone has relatively low potency for the MR, induces hyperkalemia, and is primarily eliminated via the kidney, making it unsuitable for patients with progressive renal failure.
Accordingly, there is a need for new modulators that are useful in the prevention, treatment, or amelioration of one or more of the symptoms of diseases or disorders associated with mineralocorticoid receptor activity. Such diseases or disorders include, but are not limited to fluid retention, edema, primary hyperaldosteronism, Conn's syndrome, hypertension, high blood pressure, liver cirrhosis, cardiovascular disease, heart failure, chronic heart failure, cardiac disease, renal disease, chronic kidney disease, fibrosis, and cognitive dysfunctions.